1. Field of the Invention
This invention relates to a system for a video program service, so-called Video On Demand (VOD) system, which supplies video programs utilizing a CATV system or the like in response to user's requests, and more particularly to a technique for obtaining plural reproduction signals of the same video program simultaneously from a unique video disc.
2. Description of the Prior Art
There is known a disc reproduction device having an ability to reproduce video signals from a unique video disc at different times (hereinafter referred to as "VOD reproduction"). The device of this type is equipped with a plurality of pickups for reading information and guide bars for supporting the pickups around a rotary axis of the disc. The device can reproduce a plurality of video signals simultaneously from a unique disc with a single disc rotation mechanism. It is preferable in the VOD reproduction that the video programs periodically start with approximately same time intervals between them. The interval of the program starting times is put the following limit:
Limit of time interval=(total reproduction time of the program)/(the number of the pickup device). Since the user generally wishes to watch the video program from the start, he or she needs to wait for the start of the next program. Shortening the time interval of the programs contributes to the reduction of the user's waiting time. In this view, in order to reduce the user's waiting time, it is required to equip the VOD reproduction device with as many pickup devices as possible. For example, where a video program requiring two hour reproduction time is reproduced using four pickup devices, the time interval of the starting time is a half hour (two hours/4 pickups). Namely, the same program is reproduced four times with delay times of a half hour between them.
However, in the above described VOD reproduction device, the physical shape and the structure of the pickup device put the limitation on the number of pickup device to be equipped, and therefore it is difficult to reduce the time interval of the programs beyond a certain extent. Specifically, the known reproduction device is provided with the guiding mechanism of the pickup (e.g., guide bar) on both sides of the pickup to ensure the smooth transfer of the pickup in the radial direction of the disc. Therefore, if the guide bars are arranged closely to each other so as to increase the number of the pickup device, they contact and interfere with each other in the proximity of the rotary axis of the disc due to their structural features (this phenomenon is hereinafter referred to as "interference").